This invention relates to a variable attenuator and in particular to an automatic linear compression circuit the level of attenuation of which is controlled by the input signal level.
In telephone terminals having a so-called "handsfree" capability a well-known problem is that, unless rectifying action is taken, the dial tone reproduced on the telephone terminal loudspeaker is unacceptably loud. This is because, on the one hand, the loudspeaker has to be set high enough to reproduce audibly voice signals and, on the other hand, the time averaged peak level of the dial tone is much higher than the time averaged peak level of the voice signals. Typically an automatic compressor is used to reduce selectively the signal level of the dial tone while leaving the voice level unattenuated. One drawback of prior systems is that without an increased number of components they cannot provide an acceptable range of attenuation.
Accordingly it is an object of the present invention to provide an improved form of attenuator which can easily be adapted for variable attenuation with few components.